Thursday, August 14, 2008

Hurricane Watch: Dangerous disturbance 92L poised to become a tropical depression

We're coming into the busy part of the hurricane season, it peaks around Sep. 10. Here's a post from last year: "How To Hedge A Hurricane" or you could pick up some delicious orange juice futures.
From Jeff Masters' Wunderblog:
The ominous music is rising once more, and The Joker (also known as disturbance 92L) appears poised to develop into a tropical depression today. This storm has the potential to become a hurricane that will affect the Bahama Islands and Florida early next week.

The storm fell apart yesterday, thanks to an infusion of dry air from the large region of Saharan air that continues to surround it. However, as each day goes by, 92L is moistening its environment to insulate itself from the destructive influences of this dry air. The storm is evaporating large amounts of water vapor from the warm 28-29°C waters below, then condensing this vapor inside intermittent bursts of heavy thunderstorm activity. Water vapor satellite loops show that the moistened area has steadily expanded, and is now large enough to insulate 92L from the surrounding dry air--as long as there is little wind shear. A strong jet of wind from the side could carry dry air into the core of 92L and disrupt it. However, wind shear is less than 10 knots, and this does not appear likely to happen. Visible satellite loops show some rotation at low levels, and a steadily increasing area of heavy thunderstorms. Upper-level outflow is beginning to appear to the north side....MORE

There have been some developments over the last couple weeks that increase the likelihood of tropical storms going forward:

August hurricane outlook, part I: SST's
August hurricane outlook, part II: steering currents
Major steering current shift coming; update on Lesser Antilles disturbance 92L

and from the Houston Chronicle's SciGuy, the Madden-Julian Oscillation!:
August 01, 2008
Today we're going to dig into one factor that plays a role in hurricane activity that doesn't get a whole lot of attention. But it's one that appears to have a significant impact on Gulf of Mexico tropical activity, so it's worth paying attention to.

I'm speaking of the Madden-Julian oscillation (for more detail, see here), a broad area of active cloud and rainfall that propagates eastward around the equator at intervals of between 30 to 60 days. The MJO impacts meteorological variables such as surface pressures and winds in the upper atmosphere, both of which are critical to the formation and strengthening of tropical storms.

In recent years scientists have come to better understand the general relationship between tropical storms and the MJO, publishing papers such as this one freely available from Science....MORE